This invention relates to a circuit board, and, more particularly, to a circuit board having wiring conductors provided on a semiconductor substrate having a comparatively high dielectric constant.
Where a high speed digital circuit is formed on a semiconductor substrate having a high dielectric constant such as a GaAs IC, wiring conductors are formed on the substrate for the interconnection and connection of these circuits to an external apparatus. Cross-talk noise, however, is produced between such wiring conductors. The cross-talk noise increases with increasing operation speed of the digital circuit, and the cross-talk noise increase presents problems, as discussed in Yoshihara et al, "Numerical Analysis of High Speed Pulse Transfer Characteristics in GaAs ICs", the Institute of Electronics and Communication Engineers of Japan, Research Sample SSD 83-159, (1984) p. 109, as well as in A. Masaki and T. Chiba, "Design Aspects of VLSI for Computer Logic", IEEE, J. Solid-State Circuits, Vol. SC-17, No. 2, (April 1982) pp. 381-386. As is described in this literature, cross-talk noise is pronounced when the inter-wiring capacitance is higher than the capacitance of the wiring conductor on the substrate, with respect to ground. Similar problems arise with a circuit substrate in which high speed digital ICs are provided on an insulating substrate having a high dielectric constant; e.g., alumina ceramics and IC elements interconnected by wiring conductors. In such a circuit substrate, the wiring length is frequently greater than the wiring on the GaAs substrate. Therefore, inter-wiring cross-talk noise occurs when a gentle pulse signal having a transient response is transmitted through the conductor wiring.